Conventionally, as a high-voltage bidirectional AC switch to be used in an electric power system, a bidirectional switch using MOSFET and IGBT has been known. The bidirectional switch is used in, for example, a matrix converter circuit and a neutral point clamp.
Normally, as shown in FIG. 23, a bidirectional switch 101 includes a combination of two transistors 102A and 102B and two diodes 103A and 103B. In the configuration shown in FIG. 23, the two transistors 102A and 102B are connected in series, and a conduction loss is determined by the sum of the conduction losses of the two transistors 102A and 102B, so that there is room for improvement in on-state power loss as a bidirectional switch.
Therefore, in recent years, a device having reliability in forward withstand voltage as well as in reverse withstand voltage, called a reverse blocking IGBT, has been proposed. As shown in FIG. 24, by connecting reverse blocking IGBTs 104A and 104B in parallel, a bidirectional switch 105 whose conduction loss can be calculated based on a single element can be configured.
For example, a metal film on an inner surface of a trench described in Patent Literature 1 functions as a Schottky electrode that forms a Schottky junction with an n type SIC layer. In the device described in Patent Literature 1, when a reverse voltage to cause a negative potential at a drain electrode side is applied between the drain electrode and a source electrode, the Schottky junction is caused to bear the reverse voltage.